Washington — If the first Republican presidential debate was any guide, Wednesday night’s sequel on CNN will be must-see TV. Once again, the top-polling Donald Trump will stand center stage at the Ronald Reagan presidential library in California, and 10 others – now including the GOP field’s only woman, Carly Fiorina – will flank him. Mr. Trump will have a big bull’s-eye on his back.

But everyone has something to prove in the debate, which starts at 8 p.m. Eastern. Here’s the rundown:

Trump. The celebrity billionaire has defied expectations and continued to rise in the polls since the first debate, rising as high as 33 percent among Republican primary voters against 15 other candidates.

Insulting Ms. Fiorina on her appearance? Many female Trump supporters shrug. Light on foreign policy expertise? Those were “gotcha” questions, Trump says of his interview with radio host Hugh Hewitt (who, as it happens, will be a questioner tonight). Tax hikes for hedge-fund managers? Not the GOP party line, but it strikes a populist chord with many of the party’s rank and file.

Trump can continue to do what has made him an effective candidate – such as his 90-minute stemwinder before 15,000 people in Dallas Monday night – but he also needs to get specific on policy, says Cal Jillson, a political scientist at Southern Methodist University in Dallas.

What Trump did in Dallas was “just a series of one-liners that tap into people’s doubts and concerns and rage against what government has become,” says Mr. Jillson. “But there were no real policy proposals other than, ‘It will be terrific.’ ”

Trump will need to show “a little bit of depth” if he’s challenged by the professional politicians on the debate stage, Jillson adds.

Ben Carson. The renowned neurosurgeon is nipping at Trump’s heels in the latest CBS/New York Times poll, scoring 23 percent to Trump’s 27 percent. That sets up a potential showdown Wednesday between the field’s top two outsiders. Their styles couldn’t be more different – brash Trump vs. soft-spoken Carson – but they’re both effective. Unlike the self-funding Trump, Dr. Carson needs to raise money, and a strong debate performance will boost his already-surging fundraising.

Carson also needs more air time. In the Aug. 6 debate, he seemed to get lost in the crowd until the very end, when he memorably spoke of separating conjoined twins – and about Washington’s lack of brains.

This time, Carson “has to show that he is more than a ‘one hit wonder’ if he wants to continue his surge in the polls,” writes Republican strategist Ford O’Connell in an e-mail. “Ideally, Carson wants to portray himself as the ‘adult’ outsider in contrast to Trump’s three-ring circus.”

Fiorina. Expect fireworks between Trump and the former CEO of Hewlett Packard. Fiorina’s strong performance in the “kids’ table” debate last month gave her a bump in the polls – enough to win her a promotion to the prime-time debate on Wednesday. Fiorina is still polling in single digits (4 percent) – way behind the other two “outsiders” – so she has to do well Wednesday to keep up momentum.

Trump will probably point out that Fiorina was fired by HP, and she will surely punch back. Her standard reply: "It is a leader's job to challenge the status quo, and when you do, you make enemies,” as she said in July. The question is whether Fiorina, who has never held political office, can get beyond tough talk and advance a policy agenda.

Jeb Bush. The former Florida governor entered the 2016 presidential race as the establishment favorite, and he has fallen precipitously in the polls since July (now averaging 8 percent). Trump’s taunts about “low energy” seem to have stuck. Mr. Bush still has a massive war chest – he raised $100 million in the first six months – and an extensive organization, but he needs a strong debate performance to show he can stand up to Trump’s bullying.

Scott Walker. Perhaps no candidate has underperformed against expectations as much as the governor of Wisconsin. Now at just 3.8 percent nationally, Governor Walker is rebooting his campaign by returning to familiar turf: a strong anti-union message. But the governor who won national fame by beating back public unions at home may have to be careful with a national anti-union message, at a time when working Americans are feeling beleaguered.

Marco Rubio. The junior senator from Florida has also gotten a bit lost amid Trump-mania, but he won strong reviews for his performance in the first debate and so he’s a “sleeper” – someone who could catch on if GOP voters’ love affair with outsiders fades or if Bush fails to catch on.

“He needs to show that he has the chops to be commander-in-chief,” says Mr. O’Connell. “Foreign policy questions could give Rubio that opportunity.”

John Kasich. The popular governor of Ohio is another sleeper candidate who did well in the first debate but who has been eclipsed nationally, for now, by Trump. But look at his numbers in New Hampshire, home of the critical first primary: He’s polling third, at 10.8 percent, behind Trump and Carson. A strong performance by Governor Kasich on Wednesday could boost his national numbers. Whispers of a Kasich-Rubio ticket, marrying the two biggest battleground states, Ohio and Florida, persist.

Ted Cruz. The junior senator from Texas may be one of the few on stage not gunning for Trump. They’ve formed an alliance of sorts, unusual for competing presidential candidates. (They recently co-hosted a rally opposing President Obama’s nuclear deal with Iran.) Senator Cruz’s gambit appears to be that he will pick up Trump supporters when/if the billionaire’s campaign falters.

Chris Christie. He was laid back in the first debate, leading to the question: What happened to the famously pugnacious governor of New Jersey? Governor Christie has said he didn’t feel it was appropriate to be aggressive in the first round, suggesting he will go all out in the second. His campaign is already on life support, so he’s got nothing to lose.

Rand Paul. The junior senator from Kentucky is another one hanging on by his fingernails. He and Christie tussled in the first debate, but given their respective low standings in the polls, we’re not sure that one’s worth a rerun. And with 11 people on stage Wednesday night, time will be precious.

Mike Huckabee. The former governor of Arkansas (and former Baptist preacher) gets a slice of the evangelical vote, but as the winner of the 2008 Iowa caucuses, he feels like yesterday’s news. Still, he’s bound to turn in a polished performance, as he did on Aug. 6, and that could keep him in the game a while longer.

Rick Santorum, Bobby Jindal, George Pataki, and Lindsey Graham. These four will compete in the “undercard” debate at 6 p.m. Eastern time. Governor Jindal of Louisiana has been punching hard at Trump, but we’re not sure he or any of the others will be able to pull a Fiorina and graduate to the main stage next time. Still, as long as these guys have two nickels to rub together, they probably see no reason to drop out.